This invention relates to a method for cholesterol removal in egg and egg yolk products to produce products low in cholesterol and high in polyunsaturated fat content.
Eggs have always been recognized as one of the most nutritious and popular foods. Unfortunately, egg yolk is very high in cholesterol content, comprising approximately 1.4 percent of the egg yolk weight. Furthermore, about one-third of the yolk weight is fat. Fatty acid analysis shows that the fat content of an average yolk is 35.4 percent saturated fat (principally palmitic and stearic acids), 49.1 percent monounsaturated fat (oleic acid), and 15.5 percent polyunsaturated fat (linoleic acid). Thus, the ratio of polyunsaturated fat to saturated fat is less than 1 to 2, an undesirable balance.
Substantial research effort has been directed to removal of cholesterol from egg yolks as well as food products which include these materials as ingredients. A variety of approaches to remove cholesterol from egg yolks have been tried. One approach utilizes microorganisms to enzymatically oxidize and degrade cholesterol [Japanese Patent 60-18375], but this method produces cholesterol oxidation products which may be undesirable. Organic solvents have also been used to extract cholesterol [JP 48/44458, U.S. Pat. Nos. 4,104,286; 3,881,034; 3,563,765; 4,234,619 and Tokarska, et al., Can. Inst. Food Sci. Tech. J. 18:256-258 (1985)], but such methods remove a substantial portion of the triglyceride oils, and may involve significant processing steps to remove solvents. These solvents are used to extract the cholesterol from the egg yolk. Even with supercritical carbon dioxide as the solvent, selectivity of cholesterol over triglycerides may be limited [Prepared Foods, 157:186 (1988) ; JP 59/135847]. Edible vegetable oils have also been used to extract cholesterol from egg yolks, as described in U.S. Pat. Nos. 3,717,414; 4,103,040 and 4,333,959. However, such extraction using a vegetable soybean oil to remove the cholesterol from yolk produces a waste stream of spent soybean oil. An economical process to regenerate rather than dispose of this spent oil would accordingly be desirable.
U.S. Pat. No. 4,804,555 discloses a process for the simultaneous deodorization and cholesterol level reduction of fish oils. The fish oil is deaerated, mixed with steam, heated, flash vaporized, thin film-stripped with a countercurrent stream, and cooled. U.S. Pat. No. 2,234,619 discloses a method for cholesterol removal from eggs by dehydrating the eggs, extracting the cholesterol with liquid dimethyl ether under anhydrous conditions and removing the dimethyl ether by treatment under reduced pressure at low temperatures. U.S. Pat. No. 4,104,286 describes the isolation of cholesterol from eggs through extraction with ethanol, saponification in an aqueous ethanolic alkali metal hydroxide and concentration and purification with a hydrocarbon solvent and methanol. U.S. Pat. No. 4,393,044 describes the formation of a steroid ester to be used as an oil phase material or base material for cosmetics or ointments.
Thus, it would be desirable to provide egg products having desirable functional characteristics of egg yolk products (e.g., protein and phospholipids), while reducing the cholesterol level and increasing the polyunsaturated fat to saturated fat ratio. It would further be desirable to do this while retaining the functionality, appearance and taste of natural eggs which would yield good texture upon being cooked, thus avoiding dried egg products and the like.